The basics

A blood pressure reading is made up of two numbers expressed as a fraction. The top number, or systolic pressure, measures how much pressure is in the arteries when the heart contracts. The bottom number, or diastolic pressure, measures the blood pressure between beats.

“When your heart pumps, all that blood rushes and fills your arteries,” Baker said. “It’s just like plumbing: if you’re pumping more water into the system, the pressure inside the plumbing goes up. That’s your systolic reading. When the heart relaxes and fills, the blood pressure falls and you get the lower number, or your diastolic reading.”

Which number matters more?

The answer is both. Years ago, doctors focused more on the bottom number, but it is now understood that the top number is just as important.

“Both numbers can define high blood pressure and the need for treatment,” Baker said.

A normal blood pressure is less than 120 over 80. Readings above that are now considered elevated or high. The new guidelines, which were announced last November and are based on years of data, now mean that many more Americans are categorized as having high blood pressure.

“High blood pressure is not a disease by itself, but it’s a risk factor for things like heart attack, kidney failure, stroke and more,” Baker said. “The new guidelines don’t necessarily mean that many more people have to be on medication. They just mean a very large number of people need to be aware they have elevated or high blood pressure and need to do something about it.”

Measure multiple times

One high blood pressure reading does not mean you have high blood pressure. Especially if that reading was taken minutes after you walked into a doctor’s office feeling stressed because you were late.

Patients should be relaxed and sitting quietly before a reading is taken. If the reading is high, another reading should be taken.

Baker also recommends using a blood pressure cuff at home to monitor progress of treatment. Be sure you’re relaxed and sitting, and take the average of two or three consecutive readings.

“Everybody’s blood pressure fluctuates from day to day, across times of day,” Baker said. “We’re really looking at your average trend.”

What causes high blood pressure?

Unfortunately, there’s not a simple answer. High blood pressure can be caused by anything from kidney function to blood vessel health to hormones.

“It’s really a complicated system,” Baker said. “Many things can play a part in determining a person’s blood pressure.”

That’s one reason different blood pressure medications affect different processes, such as kidney function, fluid retention and even the nervous system.

What you can do

Treatment for high blood pressure varies depending on your numbers, family history and other factors, such as whether you’ve had a heart attack or stroke, or whether you suffer from diabetes or kidney disease.

But everyone with elevated readings can benefit from lifestyle changes, such as eating a healthy diet, exercising regularly, reducing alcohol and quitting smoking.